The present invention relates generally to music-performing keyboard apparatus applicable to electronic musical instruments etc. and more particularly to an improved keyboard apparatus having an increased overall rigidity.
Music-performing keyboard apparatus, applied to electronic musical instruments etc., basically comprise a plurality of performing keys arranged side by side in a horizontal direction, Thus, the keyboard apparatus are generally elongated in shape in a direction of scale notes (i.e., key-arranged direction), so that a force produced by depression of a key during a performance acts in a direction to bend a horizontally-elongated apparatus casing as illustrated in FIG. 7. Further, when the keyboard apparatus are lifted for transfer of the keyboard apparatus, a force acts in a direction to twist the horizontally-elongated apparatus casing. For these reasons, it is desirable that the keyboard apparatus be designed to enhance the rigidity against bending (i.e., bending rigidity) and rigidity against twist (i.e., twisting rigidity) relative to the note scale (i.e., key-arrange) direction.
Typically, primary components forming a rigid structure of the keyboard apparatus are a keyboard frame and body section (casing). A plurality of keys are mounted on the keyboard frame in such a manner that they are operable (i.e., they can be caused to pivot) by a human player, and the keyboard frame is normally formed of synthetic resin, such as plastic, in order to reduce the weight of the keyboard apparatus for enhanced portability of the keyboard apparatus, reduce the manufacturing cost of the keyboard frame and meet other requirements. The body section (casing) mounts therein the keyboard frame with the keyboard mounted thereon, and this body section (casing) is also formed of synthetic resin, such as plastic, for reduced weight. The shapes and mounting structures of the frame and body section (casing) determine the rigidity of the entire keyboard apparatus.
FIG. 8 is a sectional view showing examples of shapes and mounting structures of the frame and casing in a conventional keyboard apparatus. In FIG. 8, the frame, on which are mounted a plurality of keys 1, has a concave sectional shape of a substantial inverted U opening downwardly. The frame 2 and casing 3 are fix to each other via screws 4 or the like other only along one side 2a of the opening of the frame 2, and the other side 2b of the opening of the frame 2 is supported only by abutting against the casing 3; the other side 2b is not positively fixed to the casing 3. Namely, a space defined by the downwardly-opening concave sectional shape and the casing 3 does not have a closed sectional shape, and thus, both the frame 2 and casing 3 may easily flex so that sufficient bending rigidity and twisting rigidity relative to the note scale direction is not achievable.
FIG. 9 is a sectional view showing other examples of shapes and mounting structures of the frame and casing in a conventional keyboard apparatus. The mounting structure of the frame 2 relative to the casing 3 in FIG. 9 is similar to that shown in FIG. 8, and the casing 3 has a predetermined end section 3a bent into a concavo-convex (or staggeringly-bent) structure. End surfaces of the concavo-convex structure are not positively fixed, so that the end surfaces of the concavo-convex structure tend to be detached from the frame 2. Thus, in this case too, sufficient bending rigidity and twisting rigidity relative to the scale direction is not achievable.
FIG. 10 is a sectional view showing still other examples of shapes and mounting structures of the frame and casing in a conventional keyboard apparatus. The frame 2 of a downwardly-opening concave sectional shape has a predetermined intermediate section 2c bent into a concavo-convex structure having a plurality of concave and convex portions. The frame 2 and casing 3 are fixed to each other not only along one side 2a of the opening of the frame 2 via screws 4 or the like, but also along the other side 2b of the opening of the frame 2 via screws 5 or the like. In this case, the space defined by the frame 2 and casing 3 has a closed sectional shape, but, because the closed space has a considerably great sectional area, the frame 2 and casing 3 can easily flex so that sufficient rigidity is hardly achievable. Further, although the concavo-convex structure, extending in the note scale (key-arrange) direction, can function to enhance the bending rigidity relative to the note scale (key-arrange) direction, sufficient twisting rigidity is hardly achievable because the end surfaces of the concavo-convex structure are not positively fixed. It is conceivable to reinforce the underside or the like with an external member 6 to thereby secure sufficient rigidity of the entire keyboard apparatus as illustrated in FIG. 10; however, such an approach can not said to be advisable because the provision of the reinforcing member would result in various inconveniences, such as an increased cost and increased weight.